Frequency-converted optical beams having adjustable beam characteristics

ABSTRACT

An optical beam delivery system, includes: an optical beam source; a fiber assembly situated to receive and modify one or more beam characteristics of an optical beam; and a nonlinear frequency-conversion stage in optical communication with the fiber assembly and situated to receive and frequency-convert an optical beam from a first wavelength to one or more second wavelengths. The fiber assembly includes: a first length of fiber comprising a first RIP formed to enable modification of the one or more beam characteristics of the optical beam by a perturbation device, and a second length of fiber having a second RIP coupled to the first length of fiber, the second RIP formed to confine at least a portion of modified beam characteristics of the optical beam within one or more confinement regions. The first RIP and the second RIP are different.

RELATED APPLICATIONS

This application is a continuation-in-part of international applicationPCT/US2017/034848, filed May 26, 2017, which claims the benefit of U.S.Provisional Application No. 62/401,650, filed Sep. 29, 2016. Thisapplication is a continuation-in-part of U.S. patent application Ser.No. 15/607,411, filed May 26, 2017, which claims the benefit of U.S.Provisional Application No. 62/401,650, filed Sep. 29, 2016. Thisapplication is a continuation-in-part of U.S. patent application Ser.No. 15/607,410, filed May 26, 2017, which claims the benefit of U.S.Provisional Application No. 62/401,650, filed Sep. 29, 2016. Thisapplication is a continuation-in-part of U.S. patent application Ser.No. 15/607,399, filed May 26, 2017, which claims the benefit of U.S.Provisional Application No. 62/401,650, filed Sep. 29, 2016. All of theabove applications are herein incorporated by reference in theirentireties.

TECHNICAL FIELD

The technology disclosed herein relates to fiber lasers, andfiber-coupled lasers. More particularly, the disclosed technologyrelates to methods, apparatus, and systems for adjusting and maintainingadjusted optical beam characteristics (spot size, divergence profile,spatial profile, or beam shape, or the like or any combination thereof)of a frequency-converted optical beam at an output of a fiber laser orfiber-coupled laser.

BACKGROUND

The use of high-power fiber-coupled lasers continues to gain popularityfor a variety of applications, such as materials processing, cutting,welding, and/or additive manufacturing. These lasers include, forexample, fiber lasers, disk lasers, diode lasers, diode-pumped solidstate lasers, and lamp-pumped solid state lasers. In these systems,optical power is delivered from the laser to a work piece via an opticalfiber.

Various fiber-coupled laser materials processing tasks require differentbeam characteristics (e.g., spatial profiles and/or divergenceprofiles). For example, cutting thick metal and welding generallyrequire a larger spot size than cutting thin metal. Ideally, the laserbeam properties would be adjustable to enable optimized processing forthese different tasks. Conventionally, users have two choices: (1)Employ a laser system with fixed beam characteristics that can be usedfor different tasks but is not optimal for most of them (i.e., acompromise between performance and flexibility); or (2) Purchase a lasersystem or accessories that offer variable beam characteristics but thatadd significant cost, size, weight, complexity, and perhaps performancedegradation (e.g., optical loss) or reliability degradation (e.g.,reduced robustness or up-time). Currently available laser systemscapable of varying beam characteristics require the use of free-spaceoptics or other complex and expensive add-on mechanisms (e.g., zoomlenses, mirrors, translatable or motorized lenses, combiners, etc.) inorder to vary beam characteristics. No solution exists that provides thedesired adjustability in beam characteristics that minimizes oreliminates reliance on the use of free-space optics or other extracomponents that add significant penalties in terms of cost, complexity,performance, and/or reliability.

Meanwhile, nonlinear frequency conversion is used for changing beamwavelength. As such, laser systems can incorporate nonlinear frequencyconversion in order to generate various optical harmonics of sourceradiation. In an example of a conventional nonlinear converting systemthat provides nonlinear frequency conversion, a source beam having, forexample, infrared wavelengths, is converted to visible wavelengths(e.g., green) and/or ultraviolet wavelengths.

What is needed is an in-fiber apparatus for providing varying beamcharacteristics that does not require or minimizes the use of free-spaceoptics and that can avoid significant cost, complexity, performancetradeoffs, and/or reliability degradation. Therefore, methods forcontrolling properties of lasers, while overcoming the limitations ofconventional processes and systems, to provide improved articles wouldbe a welcome addition to the art.

SUMMARY

At least disclosed herein are methods, systems and apparatus for varyingoptical beam characteristics. Methods may include, perturbing an opticalbeam propagating within a first length of fiber to adjust one or morebeam characteristics of the optical beam in the first length of fiber ora second length of fiber or a combination thereof, coupling theperturbed optical beam into a second length of fiber and maintaining atleast a portion of one or more adjusted beam characteristics within asecond length of fiber having one or more confinement regions. Methodsmay further include generating a selected output beam from the secondlength of fiber having the adjusted beam characteristics responsive to aselection of a first refractive index profile (RIP) of the first lengthof fiber or a second RIP of the second length of fiber or a combinationthereof. In some examples, the one or more beam characteristics of theperturbed optical beam are adjusted based on selection of one or morecore dimensions of the first length of fiber or one or more confinementregion dimensions of the second length of fiber or a combination thereofto generate an adjusted optical beam responsive to perturbing the firstlength of fiber, the adjusted optical beam having a particular adjusted:beam diameter, divergence distribution, beam parameter product (BPP),intensity distribution, luminance, M² value, numerical aperture (NA),optical intensity, power density, radial beam position, radiance, orspot size, or any combination thereof at an output of the second lengthof fiber. In some example, methods include perturbing the optical beamby bending the first length of fiber to alter a bend radius or alter alength of a bent region of the first length of fiber or a combinationthereof such that one or more modes of the optical beam are displacedradially with respect to a longitudinal axis of the first length offiber wherein the second length of fiber has an RIP that defines a firstconfinement region and a second confinement region. In some examples,the adjusted one or more beam characteristics are produced by confiningthe optical beam in the two or more confinement regions of the secondlength of fiber. The example methods may further comprise launching theperturbed optical beam from the first length of fiber into the firstconfinement region or the second confinement region or a combinationthereof such that one or more displaced modes of the optical beam areselectively coupled into and maintained in the first confinement regionor the second confinement region, or a combination thereof. Disclosedmethods may include, perturbing the one or more beam characteristics ofthe optical beam by perturbing the first length of fiber or the opticalbeam in the first length of fiber or a combination thereof to adjust atleast one beam characteristic of the optical beam at an output of thesecond length of fiber. Perturbing the first length of fiber may includebending, bending over a particular length, micro-bending, applyingacousto-optic excitation, thermal perturbation, stretching, or applyingpiezo-electric perturbation, or any combination thereof. The secondlength of fiber may comprise a first confinement region comprising acentral core and a second confinement region comprising an annular coreencompassing the first confinement region. Adjusting the one or morebeam characteristics of the optical beam may include selecting a RIP ofthe first length of fiber to generate a desired mode shape of a lowestorder mode, one or more higher order modes, or a combination thereofsubsequent to the adjusting. In some examples, the first length of fiberhas a core with a parabolic index profile radially spanning some or allof the core. A RIP of the first length of fiber may be selected toincrease or decrease a width of the lowest order mode, the higher ordermodes, or a combination thereof responsive to the perturbing the opticalbeam. The first length of fiber or the second length of fiber or acombination thereof may include at least one divergence structureconfigured to modify a divergence profile of the optical beam. Theconfinement regions may be separated by one or more cladding structures,wherein the divergence structure may be disposed within at least oneconfinement region separate from the cladding structure and comprisingmaterial having a lower index than the confinement region adjacent tothe divergence structure. In some examples, the second length of fibermay be azimuthally asymmetric.

Apparatus disclosed herein may include an optical beam delivery device,comprising a first length of fiber comprising a first RIP formed toenable modification of one or more beam characteristics of an opticalbeam by a perturbation device and a second length of fiber having asecond RIP coupled to the first length of fiber, the second RIP formedto confine at least a portion of the modified beam characteristics ofthe optical beam within one or more confinement regions. In someexamples, the first RIP and the second RIP are different. In someexamples, the second length of fiber comprises a plurality ofconfinement regions. The perturbation device may be coupled to the firstlength of fiber or integral with the first length of fiber or acombination thereof. The first length of fiber may comprise agraded-index RIP in at least a radially central portion and the secondlength of fiber has a first confinement region comprising a central coreand a second confinement region that is annular and encompasses thefirst confinement region. The first confinement region and the secondconfinement region may be separated by a cladding structure having arefractive index that is lower than the indexes of first confinementregion and the second confinement region. The cladding structure maycomprise a fluorosilicate material. The first length of fiber or thesecond length of fiber or a combination thereof may include at least onedivergence structure configured to modify a divergence profile of theoptical beam and wherein the divergence structure may comprise a firstmaterial having a lower index of refraction than a second materialencompassing the divergence structure. The second length of fiber may beazimuthally asymmetric and may comprise a first confinement regioncomprising a first core and a second confinement region comprising asecond core. In some examples, the first confinement region and thesecond confinement region may be coaxial. In other examples, the firstconfinement region and the second confinement region may be non-coaxial.The second confinement region may be crescent shaped in some examples.The first RIP may be parabolic in a first portion having a first radius.In some examples, the first RIP may be constant in a second portionhaving a second radius, wherein the second radius is larger than thefirst radius. The first RIP may comprise a radially graded indexextending to an edge of a core of the first length of fiber, wherein thefirst RIP is formed to increase or decrease a width of one or more modesof the optical beam responsive to the modification of the beamcharacteristics by the perturbation device. The first length of fibermay have a radially graded index core extending to a first radiusfollowed by a constant index portion extending to a second radius,wherein the second radius is larger than the first radius. In someexamples, the second length of fiber comprises a central core having adiameter in a range of about 0 to 100 microns, a first annual coreencompassing the central core having a diameter in a range of about 10to 600 microns and a second annual core having a diameter in a range ofabout 20 to 1200 microns. The perturbation device may comprise a bendingassembly configured to alter a bend radius or alter a bend length of thefirst length of fiber or a combination thereof to modify the beamcharacteristics of the optical beam. In some examples, a perturbationassembly may comprise a bending assembly, a mandrel, micro-bend in thefiber, an acousto-optic transducer, a thermal device, a fiber stretcher,or a piezo-electric device, or any combination thereof. The first lengthof fiber and the second length of fiber may be separate passive fibersthat are spliced together.

Systems disclosed herein may include, an optical beam delivery system,comprising an optical fiber including a first and second length of fiberand an optical system coupled to the second length of fiber includingone or more free-space optics configured to receive and transmit anoptical beam comprising modified beam characteristics. The first lengthof fiber may include a first RIP formed to enable, at least in part,modification of one or more beam characteristics of an optical beam by aperturbation assembly arranged to modify the one or more beamcharacteristics, the perturbation assembly may be coupled to the firstlength of fiber or integral with the first length of fiber, or acombination thereof. The second length of fiber may be coupled to thefirst length of fiber and may include a second RIP formed to preserve atleast a portion of the one or more beam characteristics of the opticalbeam modified by the perturbation assembly within one or more firstconfinement regions. In some examples, the first RIP and the second RIPare different.

The optical beam delivery system may further include a first processfiber coupled between a first process head and the optical system,wherein the first process fiber is configured to receive the opticalbeam comprising the modified one or more beam characteristics. The firstprocess fiber may comprise a third RIP configured to preserve at least aportion of the modified one or more beam characteristics of the opticalbeam within one or more second confinement regions of the first processfiber. In an example, at least a portion of the free-space optics may beconfigured to further modify the modified one or more beamcharacteristics of the optical beam. The one or more beamcharacteristics may include beam diameter, divergence distribution, BPP,intensity distribution, luminance, M² value, NA, optical intensity,power density, radial beam position, radiance, or spot size, or anycombination thereof. The third RIP may be the same as or different fromthe second RIP. The third RIP may be configured to further modify themodified one or more beam characteristics of the optical beam. In someexamples, at least one of the one or more second confinement regionsincludes at least one divergence structure configured to modify adivergence profile of the optical beam. The divergence structure maycomprise an area of lower-index material than that of the secondconfinement region.

The optical beam delivery system may further include a second processfiber having a fourth RIP that is coupled between the optical system anda second process head, wherein the second process fiber may beconfigured to receive the optical beam comprising the modified one ormore beam characteristics within one or more second confinement regionsof the second process fiber. In some examples, the first process fiberor the second process fiber or a combination thereof may be configuredto further modify the modified one or more beam characteristics of theoptical beam. The second process fiber may include at least onedivergence structure configured to modify a divergence profile of theoptical beam. The second process fiber may comprise a central coresurrounded by at least one of the one or more second confinementregions, wherein the core and the second confinement region areseparated by a cladding structure having a first index of refractionthat is lower than a second index of refraction of the central core anda third index of refraction of the second confinement region, whereinthe second confinement region may include the at least one divergencestructure. The at least one divergence structure may comprise an area oflower-index material than that of the second confinement region. In anexample, the second RIP may be different from the third RIP or thefourth RIP or a combination thereof. Alternatively, the second RIP maybe the same as the third RIP or the fourth RIP or a combination thereof.The one or more beam characteristics that may be modified can includebeam diameter, divergence distribution, BPP, intensity distribution,luminance, M² value, NA, optical intensity, power density, radial beamposition, radiance, or spot size, or any combination thereof.

In some examples, at least a portion of the free-space optics may beconfigured to further modify the modified one or more beamcharacteristics of the optical beam. The first process fiber may becoupled between a first process head and the optical system, wherein thefirst process fiber is configured to receive the optical beam comprisingtwice modified one or more beam characteristics. The first process fibermay have a third RIP configured to preserve at least a portion of thetwice modified one or more beam characteristics of the optical beamwithin one or more second confinement regions of the first processfiber. The third RIP may be different from the second RIP, wherein thethird RIP is configured to further modify the twice modified one or morebeam characteristics of the optical beam.

In some examples, the first process fiber may include a divergencestructure configured to further modify the twice modified one or morebeam characteristics of the optical beam. In some examples, a secondprocess fiber may be coupled between the optical system and a secondprocess head, wherein the second process fiber is configured to receivethe twice modified one or more beam characteristics.

In some examples, the first process fiber or the second process fiber ora combination thereof is configured to further modify the twice modifiedone or more beam characteristics of the optical beam. The first processfiber or the second process fiber or a combination thereof may includeat least one divergence structure configured to further modify the twicemodified one or more beam characteristics of the optical beam. Theoptical system may be a fiber-to-fiber coupler, a fiber-to-fiber switchor a process head, or the like or a combination thereof.

The present disclosure is further directed to a method for forming anarticle. The method comprises: providing a material comprising a firstmaterial property; forming a melt pool by exposing the material to anoptical beam comprising at least one beam characteristic, wherein themelt pool comprises at least one melt pool property determinative of asecond material property of the material; and modifying the at least onebeam characteristic in response to a change in the melt pool property.

The present disclosure is further directed to an optical beam system.The optical beam system comprises: an optical beam delivery device,comprising a first length of fiber having a first refractive-indexprofile (RIP), a second length coupled to the first length of fiber andhaving a second RIP and one or more confinement regions, and aperturbation device configured to modify one or more beamcharacteristics of an optical beam in one or more of the first length offiber and in the second length of fiber, or in the first and secondlengths of fiber, wherein the first RIP differs from the second RIP andwherein the second RIP is configured to confine at least a portion ofthe modified one or more beam characteristics of the optical beam withinthe one or more confinement regions of the second length of fiber.

The present disclosure is further directed to an optical beam system.The optical beam delivery system, comprises: an optical beam source; afiber assembly situated to receive and modify one or more beamcharacteristics of an optical beam; and a nonlinear frequency-conversionstage in optical communication with the fiber assembly and situated toreceive and frequency-convert an optical beam from a first wavelength toone or more second wavelengths. The fiber assembly includes: a firstlength of fiber comprising a first RIP formed to enable modification ofthe one or more beam characteristics of the optical beam by aperturbation device, and a second length of fiber having a second RIPcoupled to the first length of fiber, the second RIP formed to confineat least a portion of modified beam characteristics of the optical beamwithin one or more confinement regions. The first RIP and the second RIPare different.

The present disclosure is further directed to a method for manipulatingoptical beams, comprising: generating an optical beam; modifying one ormore beam characteristics of the optical beam via a fiber assembly; andfrequency converting the optical beam, wherein the fiber assemblycomprises a first length of fiber and a second length of fiber. Themodifying of the one or more beam characteristics of the optical beamcomprises: perturbing one or more of the first length of fiber and theoptical beam to adjust one or more of the beam characteristics of theoptical beam; launching the optical beam into the second length offiber; propagating the optical beam having adjusted beam characteristicsin the second length of fiber; and maintaining at least a portion of oneor more adjusted beam characteristics of the optical beam within one ormore confinement regions of the second length of fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals representlike elements, are incorporated in and constitute a part of thisspecification and, together with the description, explain the advantagesand principles of the presently disclosed technology. In the drawings,

FIG. 1 illustrates an example fiber structure for providing a laser beamhaving variable beam characteristics;

FIG. 2 depicts a cross-sectional view of an example fiber structure fordelivering a beam with variable beam characteristics;

FIG. 3 illustrates an example method of perturbing a fiber structure forproviding a beam having variable beam characteristics;

FIG. 4 is a graph illustrating the calculated spatial profile of thelowest-order mode (LP₀₁) for a first length of a fiber for differentfiber bend radii;

FIG. 5 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis nearly straight;

FIG. 6 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis bent with a radius chosen to preferentially excite a particularconfinement region of a second length of fiber;

FIGS. 7-10 depict experimental results to illustrate further outputbeams for various bend radii of a fiber for varying beam characteristicsshown in FIG. 2;

FIGS. 11-16 illustrate cross-sectional views of example first lengths offiber for enabling adjustment of beam characteristics in a fiberassembly;

FIGS. 17-19 illustrate cross-sectional views of example second lengthsof fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly;

FIGS. 20 and 21 illustrate cross-sectional views of example secondlengths of fiber for changing a divergence angle of and confining anadjusted beam in a fiber assembly configured to provide variable beamcharacteristics;

FIG. 22A illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and process head;

FIG. 22B illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and process head;

FIG. 23 illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and multiple process fibers;

FIG. 24 illustrates examples of various perturbation assemblies forproviding variable beam characteristics according to various examplesprovided herein;

FIG. 25 illustrates an example process for adjusting and maintainingmodified characteristics of an optical beam;

FIGS. 26-28 are cross-sectional views illustrating example secondlengths of fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly.

FIG. 29A illustrates an example optical beam delivery system including afiber assembly configured to provide variable beam characteristics and anonlinear frequency-conversion stage configured to frequency-adjust anoptical beam disposed between a feeding fiber and process head.

FIG. 29B illustrates an example optical beam delivery system including anonlinear frequency-conversion stage configured to frequency-adjust anoptical beam and a fiber assembly configured to provide variable beamcharacteristics disposed between a feeding fiber and process head

FIGS. 30A-30B illustrates an example process for manipulating an opticalbeam.

DETAILED DESCRIPTION

As used herein throughout this disclosure and in the claims, thesingular forms “a,” “an,” and “the” include the plural forms unless thecontext clearly dictates otherwise. Additionally, the term “includes”means “comprises.” Further, the term “coupled” does not exclude thepresence of intermediate elements between the coupled items. Also, theterms “modify” and “adjust” are used interchangeably to mean “alter.”

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

Definitions

Definitions of words and terms as used herein:

-   1. The term “beam characteristics” refers to one or more of the    following terms used to describe an optical beam. In general, the    beam characteristics of most interest depend on the specifics of the    application or optical system.-   2. The term “beam diameter” is defined as the distance across the    center of the beam along an axis for which the irradiance    (intensity) equals 1/e² of the maximum irradiance. While examples    disclosed herein generally use beams that propagate in azimuthally    symmetric modes, elliptical or other beam shapes can be used, and    beam diameter can be different along different axes. Circular beams    are characterized by a single beam diameter. Other beam shapes can    have different beam diameters along different axes.-   3. The term “spot size” is the radial distance (radius) from the    center point of maximum irradiance to the 1/e² point.-   4. The term “beam divergence distribution” is the power vs the full    cone angle. This quantity is sometimes called the “angular    distribution” or “NA distribution.”-   5. The term “beam parameter product” (BPP) of a laser beam is    defined as the product of the beam radius (measured at the beam    waist) and the beam divergence half-angle (measured in the far    field). The units of BPP are typically mm-mrad.-   6. A “confinement fiber” is defined to be a fiber that possesses one    or more confinement regions, wherein a confinement region comprises    a higher-index region (core region) surrounded by a lower-index    region (cladding region). The RIP of a confinement fiber may include    one or more higher-index regions (core regions) surrounded by    lower-index regions (cladding regions), wherein light is guided in    the higher-index regions. Each confinement region and each cladding    region can have any RIP, including but not limited to step-index and    graded-index. The confinement regions may or may not be concentric    and may be a variety of shapes such as circular, annular, polygonal,    arcuate, elliptical, or irregular, or the like or any combination    thereof. The confinement regions in a particular confinement fiber    may all have the same shape or may be different shapes. Moreover,    confinement regions may be co-axial or may have offset axes with    respect to one another. Confinement regions may be of uniform    thickness about a central axis in the longitudinal direction, or the    thicknesses may vary about the central axis in the longitudinal    direction.-   7. The term “intensity distribution” refers to optical intensity as    a function of position along a line (1D profile) or on a plane (2D    profile). The line or plane is usually taken perpendicular to the    propagation direction of the light. It is a quantitative property.-   8. “Luminance” is a photometric measure of the luminous intensity    per unit area of light travelling in a given direction.-   9. “M² factor” (also called “beam quality factor” or “beam    propagation factor”) is a dimensionless parameter for quantifying    the beam quality of laser beams, with M²=1 being a    diffraction-limited beam, and larger M2 values corresponding to    lower beam quality. M² is equal to the BPP divided by λ/π, where λ    is the wavelength of the beam in microns (if BPP is expressed in    units of mm-mrad).-   10. The term “numerical aperture” or “NA” of an optical system is a    dimensionless number that characterizes the range of angles over    which the system can accept or emit light.-   11. The term “optical intensity” is not an official (SI) unit, but    is used to denote incident power per unit area on a surface or    passing through a plane.-   12. The term “power density” refers to optical power per unit area,    although this is also referred to as “optical intensity.”-   13. The term “radial beam position” refers to the position of a beam    in a fiber measured with respect to the center of the fiber core in    a direction perpendicular to the fiber axis.-   14. “Radiance” is the radiation emitted per unit solid angle in a    given direction by a unit area of an optical source (e.g., a laser).    Radiance may be altered by changing the beam intensity distribution    and/or beam divergence profile or distribution. The ability to vary    the power density (also referred to as the radiance profile) of a    laser beam implies the ability to vary the BPP.-   15. The term “refractive-index profile” or “RIP” refers to the    refractive index as a function of position along a line (1D) or in a    plane (2D) perpendicular to the fiber axis. Many fibers are    azimuthally symmetric, in which case the 1D RIP is identical for any    azimuthal angle.-   16. A “step-index fiber” has a RIP that is flat (refractive index    independent of position) within the fiber core.-   17. A “graded-index fiber” has a RIP in which the refractive index    decreases with increasing radial position (i.e., with increasing    distance from the center of the fiber core).-   18. A “parabolic-index fiber” is a specific case of a graded-index    fiber in which the refractive index decreases quadratically with    increasing distance from the center of the fiber core.

Fiber for Varying Beam Characteristics

Disclosed herein are methods, systems, and apparatus configured toprovide a fiber operable to provide a laser beam having variable beamcharacteristics (VBC) that may reduce cost, complexity, optical loss, orother drawbacks of the conventional methods described above. This VBCfiber is configured to vary a wide variety of optical beamcharacteristics. Such beam characteristics can be controlled using theVBC fiber thus allowing users to tune various beam characteristics tosuit the particular requirements of an extensive variety of laserprocessing applications. For example, a VBC fiber may be used to tune:beam diameter, beam divergence distribution, BPP, intensitydistribution, M² factor, NA, optical intensity, power density, radialbeam position, radiance, spot size, or the like, or any combinationthereof.

In general, the disclosed technology entails coupling a laser beam intoa fiber in which the characteristics of the laser beam in the fiber canbe adjusted by perturbing the laser beam and/or perturbing a firstlength of fiber by any of a variety of methods (e.g., bending the fiberor introducing one or more other perturbations) and fully or partiallymaintaining adjusted beam characteristics in a second length of fiber.The second length of fiber is specially configured to maintain and/orfurther modify the adjusted beam characteristics. In some cases, thesecond length of fiber preserves the adjusted beam characteristicsthrough delivery of the laser beam to its ultimate use (e.g., materialsprocessing). The first and second lengths of fiber may comprise the sameor different fibers.

The disclosed technology is compatible with fiber lasers andfiber-coupled lasers. Fiber-coupled lasers typically deliver an outputvia a delivery fiber having a step-index refractive index profile (RIP),i.e., a flat or constant refractive index within the fiber core. Inreality, the RIP of the delivery fiber may not be perfectly flat,depending on the design of the fiber. Important parameters are the fibercore diameter (d_(core)) and NA. The core diameter is typically in therange of 10-1000 micron (although other values are possible), and the NAis typically in the range of 0.06-0.22 (although other values arepossible). A delivery fiber from the laser may be routed directly to theprocess head or work piece, or it may be routed to a fiber-to-fibercoupler (FFC) or fiber-to-fiber switch (FFS), which couples the lightfrom the delivery fiber into a process fiber that transmits the beam tothe process head or the work piece.

Most materials processing tools, especially those at high power (>1 kW),employ multimode (MM) fiber, but some employ single-mode (SM) fiber,which is at the lower end of the d_(core) and NA ranges. The beamcharacteristics from a SM fiber are uniquely determined by the fiberparameters. The beam characteristics from a MM fiber, however, can vary(unit-to-unit and/or as a function of laser power and time), dependingon the beam characteristics from the laser source(s) coupled into thefiber, the launching or splicing conditions into the fiber, the fiberRIP, and the static and dynamic geometry of the fiber (bending, coiling,motion, micro-bending, etc.). For both SM and MM delivery fibers, thebeam characteristics may not be optimum for a given materials processingtask, and it is unlikely to be optimum for a range of tasks, motivatingthe desire to be able to systematically vary the beam characteristics inorder to customize or optimize them for a particular processing task.

In one example, the VBC fiber may have a first length and a secondlength and may be configured to be interposed as an in-fiber devicebetween the delivery fiber and the process head to provide the desiredadjustability of the beam characteristics. To enable adjustment of thebeam, a perturbation device and/or assembly is disposed in closeproximity to and/or coupled with the VBC fiber and is responsible forperturbing the beam in a first length such that the beam'scharacteristics are altered in the first length of fiber, and thealtered characteristics are preserved or further altered as the beampropagates in the second length of fiber. The perturbed beam is launchedinto a second length of the VBC fiber configured to conserve adjustedbeam characteristics. The first and second lengths of fiber may be thesame or different fibers and/or the second length of fiber may comprisea confinement fiber. The beam characteristics that are conserved by thesecond length of VBC fiber may include any of: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity, power density, radial beam position,radiance, spot size, or the like, or any combination thereof.

FIG. 1 illustrates an example VBC fiber 100 for providing a laser beamhaving variable beam characteristics without requiring the use offree-space optics to change the beam characteristics. VBC fiber 100comprises a first length of fiber 104 and a second length of fiber 108.First length of fiber 104 and second length of fiber 108 may be the sameor different fibers and may have the same or different RIPs. The firstlength of fiber 104 and the second length of fiber 108 may be joinedtogether by a splice. First length of fiber 104 and second length offiber 108 may be coupled in other ways, may be spaced apart, or may beconnected via an interposing component such as another length of fiber,free-space optics, glue, index-matching material, or the like or anycombination thereof.

A perturbation device 110 is disposed proximal to and/or envelopsperturbation region 106. Perturbation device 110 may be a device,assembly, in-fiber structure, and/or other feature. Perturbation device110 at least perturbs optical beam 102 in first length of fiber 104 orsecond length of fiber 108 or a combination thereof in order to adjustone or more beam characteristics of optical beam 102. Adjustment of beam102 responsive to perturbation by perturbation device 110 may occur infirst length of fiber 104 or second length of fiber 108 or a combinationthereof. Perturbation region 106 may extend over various widths and mayor may not extend into a portion of second length of fiber 108. As beam102 propagates in VBC fiber 100, perturbation device 110 may physicallyact on VBC fiber 100 to perturb the fiber and adjust the characteristicsof beam 102. Alternatively, perturbation device 110 may act directly onbeam 102 to alter its beam characteristics. Subsequent to beingadjusted, perturbed beam 112 has different beam characteristics thanbeam 102, which will be fully or partially conserved in second length offiber 108. In another example, perturbation device 110 need not bedisposed near a splice. Moreover, a splice may not be needed at all, forexample VBC fiber 100 may be a single fiber, first length of fiber andsecond length of fiber could be spaced apart, or secured with a smallgap (air-spaced or filled with an optical material, such as opticalcement or an index-matching material).

Perturbed beam 112 is launched into second length of fiber 108, whereperturbed beam 112 characteristics are largely maintained or continue toevolve as perturbed beam 112 propagates yielding the adjusted beamcharacteristics at the output of second length of fiber 108. In oneexample, the new beam characteristics may include an adjusted intensitydistribution. In an example, an altered beam intensity distribution willbe conserved in various structurally bounded confinement regions ofsecond length of fiber 108. Thus, the beam intensity distribution may betuned to a desired beam intensity distribution optimized for aparticular laser processing task. In general, the intensity distributionof perturbed beam 112 will evolve as it propagates in the second lengthof fiber 108 to fill the confinement region(s) into which perturbed beam112 is launched responsive to conditions in first length of fiber 104and perturbation caused by perturbation device 110. In addition, theangular distribution may evolve as the beam propagates in the secondfiber, depending on launch conditions and fiber characteristics. Ingeneral, fibers largely preserve the input divergence distribution, butthe distribution can be broadened if the input divergence distributionis narrow and/or if the fiber has irregularities or deliberate featuresthat perturb the divergence distribution. The various confinementregions, perturbations, and fiber features of second length of fiber 108are described in greater detail below. Beams 102 and 112 are conceptualabstractions intended to illustrate how a beam may propagate through aVBC fiber 100 for providing variable beam characteristics and are notintended to closely model the behavior of a particular optical beam.

VBC fiber 100 may be manufactured by a variety of methods including PCVD(Plasma Chemical Vapor Deposition), OVD (Outside Vapor Deposition), VAD(Vapor Axial Deposition), MOCVD (Metal-Organic Chemical VaporDeposition.) and/or DND (Direct Nanoparticle Deposition). VBC fiber 100may comprise a variety of materials. For example, VBC fiber 100 maycomprise SiO₂, SiO₂ doped with GeO₂, germanosilicate, phosphoruspentoxide, phosphosilicate, Al₂O₃, aluminosilicate, or the like or anycombinations thereof. Confinement regions may be bounded by claddingdoped with fluorine, boron, or the like or any combinations thereof.Other dopants may be added to active fibers, including rare-earth ionssuch as Er³⁺ (erbium), Yb³⁺ (ytterbium), Nd³⁺ (neodymium), Tm³⁺(thulium), Ho³⁺ (holmium), or the like or any combination thereof.Confinement regions may be bounded by cladding having a lower index thanthe confinement region with fluorine or boron doping. Alternatively, VBCfiber 100 may comprise photonic crystal fibers or micro-structuredfibers.

VBC fiber 100 is suitable for use in any of a variety of fiber, fiberoptic, or fiber laser devices, including continuous wave and pulsedfiber lasers, disk lasers, solid state lasers, or diode lasers (pulserate unlimited except by physical constraints). Furthermore,implementations in a planar waveguide or other types of waveguides andnot just fibers are within the scope of the claimed technology.

FIG. 2 depicts a cross-sectional view of an example VBC fiber 200 foradjusting beam characteristics of an optical beam. In an example, VBCfiber 200 may be a process fiber because it may deliver the beam to aprocess head for material processing. VBC fiber 200 comprises a firstlength of fiber 204 spliced at junction 206 to a second length of fiber208. A perturbation assembly 210 is disposed proximal to junction 206.Perturbation assembly 210 may be any of a variety of devices configuredto enable adjustment of the beam characteristics of an optical beam 202propagating in VBC fiber 200. In an example, perturbation assembly 210may be a mandrel and/or another device that may provide means of varyingthe bend radius and/or bend length of VBC fiber 200 near the splice.Other examples of perturbation devices are discussed below with respectto FIG. 24.

In an example, first length of fiber 204 has a parabolic-index RIP 212as indicated by the left RIP graph. Most of the intensity distributionof beam 202 is concentrated in the center of fiber 204 when fiber 204 isstraight or nearly straight. Second length of fiber 208 is a confinementfiber having RIP 214 as shown in the right RIP graph. Second length offiber 208 includes confinement regions 216, 218 and 220. Confinementregion 216 is a central core surrounded by two annular (or ring-shaped)confinement regions 218 and 220. Layers 222 and 224 are structuralbarriers of lower index material between confinement regions (216, 218and 220), commonly referred to as “cladding” regions. In one example,layers 222 and 224 may comprise rings of fluorosilicate; in someembodiments, the fluorosilicate cladding layers are relatively thin.Other materials may be used as well and claimed subject matter is notlimited in this regard.

In an example, as beam 202 propagates along VBC fiber 200, perturbationassembly 210 may physically act on fiber 208 and/or beam 202 to adjustits beam characteristics and generate adjusted beam 226. In the currentexample, the intensity distribution of beam 202 is modified byperturbation assembly 210. Subsequent to adjustment of beam 202 theintensity distribution of adjusted beam 226 may be concentrated in outerconfinement regions 218 and 220 with relatively little intensity in thecentral confinement region 216. Because each of confinement regions 216,218, and/or 220 is isolated by the thin layers of lower index materialin barrier layers 222 and 224, second length of fiber 208 cansubstantially maintain the adjusted intensity distribution of adjustedbeam 226. The beam will typically become distributed azimuthally withina given confinement region but will not transition (significantly)between the confinement regions as it propagates along the second lengthof fiber 208. Thus, the adjusted beam characteristics of adjusted beam226 are largely conserved within the isolated confinement regions 216,218, and/or 220. In some cases, it be may desirable to have the beam 226power divided among the confinement regions 216, 218, and/or 220 ratherthan concentrated in a single region, and this condition may be achievedby generating an appropriately adjusted beam 226.

In one example, core confinement region 216 and annular confinementregions 218 and 220 may be composed of fused silica glass, and cladding222 and 224 defining the confinement regions may be composed offluorosilicate glass. Other materials may be used to form the variousconfinement regions (216, 218 and 220), including germanosilicate,phosphosilicate, aluminosilicate, or the like, or a combination thereofand claimed subject matter is not so limited. Other materials may beused to form the barrier rings (222 and 224), including fused silica,borosilicate, or the like or a combination thereof, and claimed subjectmatter is not so limited. In other embodiments, the optical fibers orwaveguides include or are composed of various polymers or plastics orcrystalline materials. Generally, the core confinement regions haverefractive indices that are greater than the refractive indices ofadjacent barrier/cladding regions.

In some examples, it may be desirable to increase a number ofconfinement regions in a second length of fiber to increase granularityof beam control over beam displacements for fine-tuning a beam profile.For example, confinement regions may be configured to provide stepwisebeam displacement.

FIG. 3 illustrates an example method of perturbing fiber 200 forproviding variable beam characteristics of an optical beam. Changing thebend radius of a fiber may change the radial beam position, divergenceangle, and/or radiance profile of a beam within the fiber. The bendradius of VBC fiber 200 can be decreased from a first bend radius R₁ toa second bend radius R₂ about splice junction 206 by using a steppedmandrel or cone as the perturbation assembly 210. Additionally oralternatively, the engagement length on the mandrel(s) or cone can bevaried. Rollers 250 may be employed to engage VBC fiber 200 acrossperturbation assembly 210. In an example, an amount of engagement ofrollers 250 with fiber 200 has been shown to shift the distribution ofthe intensity profile to the outer confinement regions 218 and 220 offiber 200 with a fixed mandrel radius. There are a variety of othermethods for varying the bend radius of fiber 200, such as using aclamping assembly, flexible tubing, or the like, or a combinationthereof, and claimed subject matter is not limited in this regard. Inanother example, for a particular bend radius the length over which VBCfiber 200 is bent can also vary beam characteristics in a controlled andreproducible way. In examples, changing the bend radius and/or lengthover which the fiber is bent at a particular bend radius also modifiesthe intensity distribution of the beam such that one or more modes maybe shifted radially away from the center of a fiber core.

Maintaining the bend radius of the fibers across junction 206 ensuresthat the adjusted beam characteristics such as radial beam position andradiance profile of optical beam 202 will not return to beam 202'sunperturbed state before being launched into second length of fiber 208.Moreover, the adjusted radial beam characteristics, including position,divergence angle, and/or intensity distribution, of adjusted beam 226can be varied based on an extent of decrease in the bend radius and/orthe extent of the bent length of VBC fiber 200. Thus, specific beamcharacteristics may be obtained using this method.

In the current example, first length of fiber 204 having first RIP 212is spliced at junction 206 to a second length of fiber 208 having asecond RIP 214. However, it is possible to use a single fiber having asingle RIP formed to enable perturbation (e.g., by micro-bending) of thebeam characteristics of beam 202 and also to enable conservation of theadjusted beam. Such a RIP may be similar to the RIPs shown in fibersillustrated in FIGS. 17, 18, and/or 19.

FIGS. 7-10 provide experimental results for VBC fiber 200 (shown inFIGS. 2 and 3) and illustrate further a beam response to perturbation ofVBC fiber 200 when a perturbation assembly 210 acts on VBC fiber 200 tobend the fiber. FIGS. 4-6 are simulations and FIGS. 7-10 areexperimental results wherein a beam from a SM 1050 nm source waslaunched into an input fiber (not shown) with a 40 micron core diameter.The input fiber was spliced to first length of fiber 204.

FIG. 4 is an example graph 400 illustrating the calculated profile ofthe lowest-order mode (LP₀₁) for a first length of fiber 204 fordifferent fiber bend radii 402, wherein a perturbation assembly 210involves bending VBC fiber 200. As the fiber bend radius is decreased,an optical beam propagating in VBC fiber 200 is adjusted such that themode shifts radially away from the center 404 of a VBC fiber 200 core(r=0 micron) toward the core/cladding interface (located at r=100 micronin this example). Higher-order modes (LP_(In)) also shift with bending.Thus, a straight or nearly straight fiber (very large bend radius),curve 406 for LP₀₁ is centered at or near the center 404 of VBC fiber200. At a bend radius of about 6 cm, curve 408 for LP₀₁ is shifted to aradial position of about 40 μm from the center 406 of VBC fiber 200. Ata bend radius of about 5 cm, curve 410 for LP₀₁ is shifted to a radialposition about 50 μm from the center 404 of VBC fiber 200. At a bendradius of about 4 cm, curve 412 for LP₀₁ is shifted to a radial positionabout 60 μm from the center 404 of VBC fiber 200. At a bend radius ofabout 3 cm, curve 414 for LP₀₁ is shifted to a radial position about 80μm from the center 404 of VBC fiber 200. At a bend radius of about 2.5cm, a curve 416 for LP₀₁ is shifted to a radial position about 85 μmfrom the center 404 of VBC fiber 200. Note that the shape of the moderemains relatively constant (until it approaches the edge of the core),which is a specific property of a parabolic RIP. Although, this propertymay be desirable in some situations, it is not required for the VBCfunctionality, and other RIPs may be employed.

In an example, if VBC fiber 200 is straightened, LP₀₁ mode will shiftback toward the center of the fiber. Thus, the purpose of second lengthof fiber 208 is to “trap” or confine the adjusted intensity distributionof the beam in a confinement region that is displaced from the center ofthe VBC fiber 200. The splice between fibers 204 and 208 is included inthe bent region, thus the shifted mode profile will be preferentiallylaunched into one of the ring-shaped confinement regions 218 and 220 orbe distributed among the confinement regions. FIGS. 5 and 6 illustratethis effect.

FIG. 5 illustrates an example two-dimensional intensity distribution atjunction 206 within second length of fiber 208 when VBC fiber 200 isnearly straight. A significant portion of LP₀₁ and LP_(In) are withinconfinement region 216 of fiber 208. FIG. 6 illustrates thetwo-dimensional intensity distribution at junction 206 within secondlength of fiber 208 when VBC fiber 200 is bent with a radius chosen topreferentially excite confinement region 220 (the outermost confinementregion) of second length of fiber 208. A significant portion of LP₀₁ andLP_(In) are within confinement region 220 of fiber 208.

In an example, second length of fiber 208 confinement region 216 has a100 micron diameter, confinement region 218 is between 120 micron and200 micron in diameter, and confinement region 220 is between 220 micronand 300 micron diameter. Confinement regions 216, 218, and 220 areseparated by 10 um thick rings of fluorosilicate, providing an NA of0.22 for the confinement regions. Other inner and outer diameters forthe confinement regions, thicknesses of the rings separating theconfinement regions, NA values for the confinement regions, and numbersof confinement regions may be employed.

Referring again to FIG. 5, with the noted parameters, when VBC fiber 200is straight about 90% of the power is contained within the centralconfinement region 216, and about 100% of the power is contained withinconfinement regions 216 and 218. Referring now to FIG. 6, when fiber 200is bent to preferentially excite second ring confinement region 220,nearly 75% of the power is contained within confinement region 220, andmore than 95% of the power is contained within confinement regions 218and 220. These calculations include LP₀₁ and two higher-order modes,which is typical in some 2-4 kW fiber lasers.

It is clear from FIGS. 5 and 6 that in the case where a perturbationassembly 210 acts on VBC fiber 200 to bend the fiber, the bend radiusdetermines the spatial overlap of the modal intensity distribution ofthe first length of fiber 204 with the different guiding confinementregions (216, 218, and 220) of the second length of fiber 208. Changingthe bend radius can thus change the intensity distribution at the outputof the second length of fiber 208, thereby changing the diameter or spotsize of the beam, and thus also changing its radiance and BPP value.This adjustment of the spot size may be accomplished in an all-fiberstructure, involving no free-space optics and consequently may reduce oreliminate the disadvantages of free-space optics discussed above. Suchadjustments can also be made with other perturbation assemblies thatalter bend radius, bend length, fiber tension, temperature, or otherperturbations discussed below.

In a typical materials processing system (e.g., a cutting or weldingtool), the output of the process fiber is imaged at or near the workpiece by the process head. Varying the intensity distribution as shownin FIGS. 5 and 6 thus enables variation of the beam profile at the workpiece in order to tune and/or optimize the process, as desired. SpecificRIPs for the two fibers were assumed for the purpose of the abovecalculations, but other RIPs are possible, and claimed subject matter isnot limited in this regard.

FIGS. 7-10 depict experimental results (measured intensitydistributions) to illustrate further output beams for various bend radiiof VBC fiber 200 shown in FIG. 2.

In FIG. 7 when VBC fiber 200 is straight, the beam is nearly completelyconfined to confinement region 216. As the bend radius is decreased, theintensity distribution shifts to higher diameters (FIGS. 8-10). FIG. 8depicts the intensity distribution when the bend radius of VBC fiber 200is chosen to shift the intensity distribution preferentially toconfinement region 218. FIG. 9 depicts the experimental results when thebend radius is further reduced and chosen to shift the intensitydistribution outward to confinement region 220 and confinement region218. In FIG. 10, at the smallest bend radius, the beam is nearly a“donut mode”, with most of the intensity in the outermost confinementregion 220.

Despite excitation of the confinement regions from one side at thesplice junction 206, the intensity distributions are nearly symmetricazimuthally because of scrambling within confinement regions as the beampropagates within the VBC fiber 200. Although the beam will typicallyscramble azimuthally as it propagates, various structures orperturbations (e.g., coils) could be included to facilitate thisprocess.

For the fiber parameters used in the experiment shown in FIGS. 7-10,particular confinement regions were not exclusively excited because someintensity was present in multiple confinement regions. This feature mayenable advantageous materials processing applications that are optimizedby having a flatter or distributed beam intensity distribution. Inapplications requiring cleaner excitation of a given confinement region,different fiber RIPs could be employed to enable this feature.

The results shown in FIGS. 7-10 pertain to the particular fibers used inthis experiment, and the details will vary depending on the specifics ofthe implementation. In particular, the spatial profile and divergencedistribution of the output beam and their dependence on bend radius willdepend on the specific RIPs employed, on the splice parameters, and onthe characteristics of the laser source launched into the first fiber.

Different fiber parameters than those shown in FIG. 2 may be used andstill be within the scope of the claimed subject matter. Specifically,different RIPs and core sizes and shapes may be used to facilitatecompatibility with different input beam profiles and to enable differentoutput beam characteristics. Example RIPs for the first length of fiber,in addition to the parabolic-index profile shown in FIG. 2, includeother graded-index profiles, step-index, pedestal designs (i.e., nestedcores with progressively lower refractive indices with increasingdistance from the center of the fiber), and designs with nested coreswith the same refractive index value but with various NA values for thecentral core and the surrounding rings. Example RIPs for the secondlength of fiber, in addition to the profile shown in FIG. 2, includeconfinement fibers with different numbers of confinement regions,non-uniform confinement-region thicknesses, different and/or non-uniformvalues for the thicknesses of the rings surrounding the confinementregions, different and/or non-uniform NA values for the confinementregions, different refractive-index values for the high-index andlow-index portions of the RIP, non-circular confinement regions (such aselliptical, oval, polygonal, square, rectangular, or combinationsthereof), as well as other designs as discussed in further detail withrespect to FIGS. 26-28. Furthermore, VBC fiber 200 and other examples ofa VBC fiber described herein are not restricted to use of two fibers. Insome examples, implementation may include use of one fiber or more thantwo fibers. In some cases, the fiber(s) may not be axially uniform; forexample, they could include fiber Bragg gratings or long-periodgratings, or the diameter could vary along the length of the fiber. Inaddition, the fibers do not have to be azimuthally symmetric, e.g., thecore(s) could have square or polygonal shapes. Various fiber coatings(buffers) may be employed, including high-index or index-matchedcoatings (which strip light at the glass-polymer interface) andlow-index coatings (which guide light by total internal reflection atthe glass-polymer interface). In some examples, multiple fiber coatingsmay be used on VBC fiber 200.

FIGS. 11-16 illustrate cross-sectional views of examples of firstlengths of fiber for enabling adjustment of beam characteristics in aVBC fiber responsive to perturbation of an optical beam propagating inthe first lengths of fiber. Some examples of beam characteristics thatmay be adjusted in the first length of fiber are: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity profile, power density profile, radialbeam position, radiance, spot size, or the like, or any combinationthereof. The first lengths of fiber depicted in FIGS. 11-16 anddescribed below are merely examples and do not provide an exhaustiverecitation of the variety of first lengths of fiber that may be utilizedto enable adjustment of beam characteristics in a VBC fiber assembly.Selection of materials, appropriate RIPs, and other variables for thefirst lengths of fiber illustrated in FIGS. 11-16 at least depend on adesired beam output. A wide variety of fiber variables are contemplatedand are within the scope of the claimed subject matter. Thus, claimedsubject matter is not limited by examples provided herein.

In FIG. 11 first length of fiber 1100 comprises a step-index profile1102. FIG. 12 illustrates a first length of fiber 1200 comprising a“pedestal RIP” (i.e., a core comprising a step-index region surroundedby a larger step-index region) 1202. FIG. 13 illustrates first length offiber 1300 comprising a multiple-pedestal RIP 1302.

FIG. 14A illustrates first length of fiber 1400 comprising agraded-index profile 1418 surrounded by a down-doped region 1404. Fiber1400 has a RIP 1402. When the fiber 1400 is perturbed, modes may shiftradially outward in fiber 1400 (e.g., during bending of fiber 1400).Graded-index profile 1418 may be designed to promote maintenance or evencompression of modal shape. This design may promote adjustment of a beampropagating in fiber 1400 to generate a beam having a beam intensitydistribution concentrated in an outer perimeter of the fiber (i.e., in aportion of the fiber core that is displaced from the fiber axis). Asdescribed above, when the adjusted beam is coupled into a second lengthof fiber having confinement regions, the intensity distribution of theadjusted beam may be trapped in the outermost confinement region,providing a donut shaped intensity distribution. A beam spot having anarrow outer confinement region may be useful to enable certain materialprocessing actions.

FIG. 14B illustrates first length of fiber 1406 comprising agraded-index profile 1414 surrounded by a down-doped region 1408 similarto fiber 1400. However, fiber 1406 includes a divergence structure 1410(a lower-index region) as can be seen in RIP 1412. The divergencestructure 1410 is an area of material with a lower refractive index thanthat of the surrounding core. As the beam is launched into first lengthof fiber 1406, refraction from divergence structure 1410 causes the beamdivergence to increase in first length of fiber 1406. The amount ofincreased divergence depends on the amount of spatial overlap of thebeam with the divergence structure 1410 and the magnitude of the indexdifference between the divergence structure 1410 and the core material.Divergence structure 1410 can have a variety of shapes, depending on theinput divergence distribution and desired output divergencedistribution. In an example, divergence structure 1410 has a triangularor graded index shape.

FIG. 15 illustrates a first length of fiber 1500 comprising aparabolic-index central region 1502 surrounded by a constant-indexregion 1504, and the constant-index region 1504 is surrounded by alower-index annular layer 1506. The lower-index annular layer 1506 helpsguide a beam propagating in fiber 1500. When the propagating beam isperturbed, modes shift radially outward in fiber 1500 (e.g., duringbending of fiber 1500). As one or more modes shift radially outward,parabolic-index region 1502 promotes retention of modal shape. When themodes reach the constant-index region 1504 of the RIP 1510, they will becompressed against the low-index annular layer 1506, which may causepreferential excitation of the outermost confinement region in thesecond fiber (in comparison to the first fiber RIP shown in FIG. 14). Inone implementation, this fiber design works with a confinement fiberhaving a central step-index core and a single annular core. Theparabolic-index portion 1502 of the RIP overlaps with the centralstep-index core of the confinement fiber. The constant-index portion1504 overlaps with the annular core of the confinement fiber. Theconstant-index portion 1504 of the first fiber is intended to make iteasier to move the beam into overlap with the annular core by bending.This fiber design also works with other designs of the confinementfiber.

FIG. 16 illustrates a first length of fiber 1600 comprising guidingregions 1604, 1606, 1608, and 1616 bounded by lower-index layers 1610,1612, and 1614 where the indexes of the lower-index layers 1610, 1612,and 1614 are stepped or, more generally, do not all have the same valueas illustrated by RIP 1602.The lower-index layers may serve to bound thebeam intensity to certain guiding regions (1604, 1606, 1608, and 1616)when the perturbation assembly 210 (see FIG. 2) acts on the fiber 1600.In this way, adjusted beam light may be trapped in the guiding regionsover a range of perturbation actions (such as over a range of bendradii, a range of bend lengths, a range of micro-bending pressures,and/or a range of acousto-optical signals), allowing for a certaindegree of perturbation tolerance before a beam intensity distribution isshifted to a more distant radial position in fiber 1600. Thus, variationin beam characteristics may be controlled in a step-wise fashion. Theradial widths of the guiding regions 1604, 1606, 1608, and 1616 may beadjusted to achieve a desired ring width, as may be required by anapplication. Also, a guiding region can have a thicker radial width tofacilitate trapping of a larger fraction of the incoming beam profile ifdesired. Region 1606 is an example of such a design.

FIGS. 17-21 depict examples of fibers configured to enable maintenanceand/or confinement of adjusted beam characteristics in the second lengthof fiber (e.g., fiber 208). These fiber designs are referred to as“ring-shaped confinement fibers” because they contain a central coresurrounded by annular or ring-shaped cores. These designs are merelyexamples and not an exhaustive recitation of the variety of fiber RIPsthat may be used to enable maintenance and/or confinement of adjustedbeam characteristics within a fiber. Thus, claimed subject matter is notlimited to the examples provided herein. Moreover, any of the firstlengths of fiber described above with respect to FIGS. 11-16 may becombined with any of the second length of fiber described FIGS. 17-21.

FIG. 17 illustrates a cross-sectional view of an example second lengthof fiber for maintaining and/or confining adjusted beam characteristicsin a VBC fiber assembly. As the perturbed beam is coupled from a firstlength of fiber to second length of fiber 1700, the second length offiber 1700 may maintain at least a portion of the beam characteristicsadjusted in response to perturbation in the first length of fiber withinone or more of confinement regions 1704, 1706, and/or 1708. Fiber 1700has a RIP 1702. Each of confinement regions 1704, 1706, and/or 1708 isbounded by a lower index layer 1710 and/or 1712. This design enablessecond length of fiber 1700 to maintain the adjusted beamcharacteristics. As a result, a beam output by fiber 1700 willsubstantially maintain the received adjusted beam as modified in thefirst length of fiber giving the output beam adjusted beamcharacteristics, which may be customized to a processing task or otherapplication.

Similarly, FIG. 18 depicts a cross-sectional view of an example secondlength of fiber 1800 for maintaining and/or confining beamcharacteristics adjusted in response to perturbation in the first lengthof fiber in a VBC fiber assembly. Fiber 1800 has a RIP 1802. However,confinement regions 1808, 1810, and/or 1812 have different thicknessesthan confinement regions 1704, 1706, and 1708. Each of confinementregions 1808, 1810, and/or 1812 is bounded by a lower index layer 1804and/or 1806. Varying the thicknesses of the confinement regions (and/orbarrier regions) enables tailoring or optimization of a confinedadjusted radiance profile by selecting particular radial positionswithin which to confine an adjusted beam.

FIG. 19 depicts a cross-sectional view of an example second length offiber 1900 having a RIP 1902 for maintaining and/or confining anadjusted beam in a VBC fiber assembly configured to provide variablebeam characteristics. In this example, the number and thicknesses ofconfinement regions 1904, 1906, 1908, and 1910 are different from fiber1700 and 1800 and the barrier layers 1912, 1914, and 1916 are of variedthicknesses as well. Furthermore, confinement regions 1904, 1906, 1908,and 1910 have different indexes of refraction and barrier layers 1912,1914, and 1916 have different indexes of refraction as well. This designmay further enable a more granular or optimized tailoring of theconfinement and/or maintenance of an adjusted beam radiance toparticular radial locations within fiber 1900. As the perturbed beam islaunched from a first length of fiber to second length of fiber 1900 themodified beam characteristics of the beam (having an adjusted intensitydistribution, radial position, and/or divergence angle, or the like, ora combination thereof) is confined within a specific radius by one ormore of confinement regions 1904, 1906, 1908 and/or 1910 of secondlength of fiber 1900.

As noted previously, the divergence angle of a beam may be conserved oradjusted and then conserved in the second length of fiber. There are avariety of methods to change the divergence angle of a beam. Thefollowing are examples of fibers configured to enable adjustment of thedivergence angle of a beam propagating from a first length of fiber to asecond length of fiber in a fiber assembly for varying beamcharacteristics. However, these are merely examples and not anexhaustive recitation of the variety of methods that may be used toenable adjustment of divergence of a beam. Thus, claimed subject matteris not limited to the examples provided herein.

FIG. 20 depicts a cross-sectional view of an example second length offiber 2000 having RIP 2002 for modifying, maintaining, and/or confiningbeam characteristics adjusted in response to perturbation in the firstlength of fiber. In this example, second length of fiber 2000 is similarto the previously described second lengths of fiber and forms a portionof the VBC fiber assembly for delivering variable beam characteristicsas discussed above. There are three confinement regions 2004, 2006, and2008 and three barrier layers 2010, 2012, and 2016. Second length offiber 2000 also has a divergence structure 2014 situated within theconfinement region 2006. The divergence structure 2014 is an area ofmaterial with a lower refractive index than that of the surroundingconfinement region. As the beam is launched into second length of fiber2000 refraction from divergence structure 2014 causes the beamdivergence to increase in second length of fiber 2000. The amount ofincreased divergence depends on the amount of spatial overlap of thebeam with the divergence structure 2014 and the magnitude of the indexdifference between the divergence structure 2014 and the core material.By adjusting the radial position of the beam near the launch point intothe second length of fiber 2000, the divergence distribution may bevaried. The adjusted divergence of the beam is conserved in fiber 2000,which is configured to deliver the adjusted beam to the process head,another optical system (e.g., fiber-to-fiber coupler or fiber-to-fiberswitch), the work piece, or the like, or a combination thereof. In anexample, divergence structure 2014 may have an index dip of about10⁻⁵-3×10⁻² with respect to the surrounding material. Other values ofthe index dip may be employed within the scope of this disclosure andclaimed subject matter is not so limited.

FIG. 21 depicts a cross-sectional view of an example second length offiber 2100 having a RIP 2102 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. Second length of fiber 2100 forms a portionof a VBC fiber assembly for delivering a beam having variablecharacteristics. In this example, there are three confinement regions2104, 2106, and 2108 and three barrier layers 2110, 2112, and 2116.Second length of fiber 2100 also has a plurality of divergencestructures 2114 and 2118. The divergence structures 2114 and 2118 areareas of graded lower index material. As the beam is launched from thefirst length fiber into second length of fiber 2100, refraction fromdivergence structures 2114 and 2118 causes the beam divergence toincrease. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure and themagnitude of the index difference between the divergence structure 2114and/or 2118 and the surrounding core material of confinement regions2106 and 2104 respectively. By adjusting the radial position of the beamnear the launch point into the second length of fiber 2100, thedivergence distribution may be varied. The design shown in FIG. 21allows the intensity distribution and the divergence distribution to bevaried somewhat independently by selecting both a particular confinementregion and the divergence distribution within that conferment region(because each confinement region may include a divergence structure).The adjusted divergence of the beam is conserved in fiber 2100, which isconfigured to deliver the adjusted beam to the process head, anotheroptical system, or the work piece. Forming the divergence structures2114 and 2118 with a graded or non-constant index enables tuning of thedivergence profile of the beam propagating in fiber 2100. An adjustedbeam characteristic such as a radiance profile and/or divergence profilemay be conserved as it is delivered to a process head by the secondfiber. Alternatively, an adjusted beam characteristic such as a radianceprofile and/or divergence profile may be conserved or further adjustedas it is routed by the second fiber through a fiber-to-fiber coupler(FFC) and/or fiber-to-fiber switch (FFS) and to a process fiber, whichdelivers the beam to the process head or the work piece.

FIGS. 26-28 are cross-sectional views illustrating examples of fibersand fiber RIPs configured to enable maintenance and/or confinement ofadjusted beam characteristics of a beam propagating in an azimuthallyasymmetric second length of fiber wherein the beam characteristics areadjusted responsive to perturbation of a first length of fiber coupledto the second length of fiber and/or perturbation of the beam by aperturbation device 110. These azimuthally asymmetric designs are merelyexamples and are not an exhaustive recitation of the variety of fiberRIPs that may be used to enable maintenance and/or confinement ofadjusted beam characteristics within an azimuthally asymmetric fiber.Thus, claimed subject matter is not limited to the examples providedherein. Moreover, any of a variety of first lengths of fiber (e.g., likethose described above) may be combined with any azimuthally asymmetricsecond length of fiber (e.g., like those described in FIGS. 26-28).

FIG. 26 illustrates RIPs at various azimuthal angles of a cross-sectionthrough an elliptical fiber 2600. At a first azimuthal angle 2602, fiber2600 has a first RIP 2604. At a second azimuthal angle 2606 that isrotated 45° from first azimuthal angle 2602, fiber 2600 has a second RIP2608. At a third azimuthal angle 2610 that is rotated another 45° fromsecond azimuthal angle 2606, fiber 2600 has a third RIP 2612. First,second and third RIPs 2604, 2608 and 2612 are all different.

FIG. 27 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a multicore fiber 2700. At a first azimuthal angle 2702, fiber2700 has a first RIP 2704. At a second azimuthal angle 2706, fiber 2700has a second RIP 2708. First and second RIPs 2704 and 2708 aredifferent. In an example, perturbation device 110 may act in multipleplanes in order to launch the adjusted beam into different regions of anazimuthally asymmetric second fiber.

FIG. 28 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a fiber 2800 having at least one crescent shaped core. In somecases, the corners of the crescent may be rounded, flattened, orotherwise shaped, which may minimize optical loss. At a first azimuthalangle 2802, fiber 2800 has a first RIP 2804. At a second azimuthal angle2806, fiber 2800 has a second RIP 2808. First and second RIPs 2804 and2808 are different.

FIG. 22A illustrates an example of a laser system 2200 including a VBCfiber assembly 2202 configured to provide variable beam characteristics.VBC fiber assembly 2202 comprises a first length of fiber 104, secondlength of fiber 108, and a perturbation device 110. VBC fiber assembly2202 is disposed between feeding fiber 2212 (i.e., the output fiber fromthe laser source) and VBC delivery fiber 2240. VBC delivery fiber 2240may comprise second length of fiber 108 or an extension of second lengthof fiber 108 that modifies, maintains, and/or confines adjusted beamcharacteristics. Beam 2210 is coupled into VBC fiber assembly 2202 viafeeding fiber 2212. Fiber assembly 2202 is configured to vary thecharacteristics of beam 2210 in accordance with the various examplesdescribed above. The output of fiber assembly 2202 is adjusted beam 2214which is coupled into VBC delivery fiber 2240. VBC delivery fiber 2240delivers adjusted beam 2214 to free-space optics assembly 2208, whichthen couples beam 2214 into a process fiber 2204. Adjusted beam 2214 isthen delivered to process head 2206 by process fiber 2204. The processhead can include guided wave optics (such as fibers and fiber coupler),free space optics such as lenses, mirrors, optical filters, diffractiongratings), beam scan assemblies such as galvanometer scanners, polygonalmirror scanners, or other scanning systems that are used to shape thebeam 2214 and deliver the shaped beam to a workpiece.

In laser system 2200, one or more of the free-space optics of assembly2208 may be disposed in an FFC or other beam coupler 2216 to perform avariety of optical manipulations of an adjusted beam 2214 (representedin FIG. 22A with different dashing than beam 2210). For example,free-space optics assembly 2208 may preserve the adjusted beamcharacteristics of beam 2214. Process fiber 2204 may have the same RIPas VBC delivery fiber 2240. Thus, the adjusted beam characteristics ofadjusted beam 2214 may be preserved all the way to process head 2206.Process fiber 2204 may comprise a RIP similar to any of the secondlengths of fiber described above, including confinement regions.

Alternatively, as illustrated in FIG. 22B, free-space optics assembly2208 may change the adjusted beam characteristics of beam 2214 by, forexample, increasing or decreasing the divergence and/or the spot size ofbeam 2214 (e.g., by magnifying or demagnifying beam 2214) and/orotherwise further modifying adjusted beam 2214. Furthermore, processfiber 2204 may have a different RIP than VBC delivery fiber 2240.Accordingly, the RIP of process fiber 2204 may be selected to preserveadditional adjustment of adjusted beam 2214 made by the free-spaceoptics of assembly 2208 to generate a twice adjusted beam 2224(represented in FIG. 22B with different dashing than beam 2214).

FIG. 23 illustrates an example of a laser system 2300 including VBCfiber assembly 2302 disposed between feeding fiber 2312 and VBC deliveryfiber 2340. During operation, beam 2310 is coupled into VBC fiberassembly 2302 via feeding fiber 2312. Fiber assembly 2302 includes afirst length of fiber 104, second length of fiber 108, and aperturbation device 110 and is configured to vary characteristics ofbeam 2310 in accordance with the various examples described above. Fiberassembly 2302 generates adjusted beam 2314 output by VBC delivery fiber2340. VBC delivery fiber 2340 comprises a second length of fiber 108 offiber for modifying, maintaining, and/or confining adjusted beamcharacteristics in a fiber assembly 2302 in accordance with the variousexamples described above (see FIGS. 17-21, for example). VBC deliveryfiber 2340 couples adjusted beam 2314 into beam switch (FFS) 2332, whichthen couples its various output beams to one or more of multiple processfibers 2304, 2320, and 2322. Process fibers 2304, 2320, and 2322 deliveradjusted beams 2314, 2328, and 2330 to respective process heads 2306,2324, and 2326.

In an example, beam switch 2332 includes one or more sets of free-spaceoptics 2308, 2316, and 2318 configured to perform a variety of opticalmanipulations of adjusted beam 2314. Free-space optics 2308, 2316, and2318 may preserve or vary adjusted beam characteristics of beam 2314.Thus, adjusted beam 2314 may be maintained by the free-space optics oradjusted further. Process fibers 2304, 2320, and 2322 may have the sameor a different RIP as VBC delivery fiber 2340, depending on whether itis desirable to preserve or further modify a beam passing from thefree-space optics assemblies 2308, 2316, and 2318 to respective processfibers 2304, 2320, and 2322. In other examples, one or more beamportions of beam 2310 are coupled to a workpiece without adjustment, ordifferent beam portions are coupled to respective VBC fiber assembliesso that beam portions associated with a plurality of beamcharacteristics can be provided for simultaneous workpiece processing.Alternatively, beam 2310 can be switched to one or more of a set of VBCfiber assemblies.

Routing adjusted beam 2314 through any of free-space optics assemblies2308, 2316, and 2318 enables delivery of a variety of additionallyadjusted beams to process heads 2306, 2324, and 2326. Therefore, lasersystem 2300 provides additional degrees of freedom for varying thecharacteristics of a beam, as well as switching the beam between processheads (“time sharing”) and/or delivering the beam to multiple processheads simultaneously (“power sharing”).

For example, free-space optics in beam switch 2332 may direct adjustedbeam 2314 to free-space optics assembly 2316 configured to preserve theadjusted characteristics of beam 2314. Process fiber 2304 may have thesame RIP as VBC delivery fiber 2340. Thus, the beam delivered to processhead 2306 will be a preserved adjusted beam 2314.

In another example, beam switch 2332 may direct adjusted beam 2314 tofree-space optics assembly 2318 configured to preserve the adjustedcharacteristics of adjusted beam 2314. Process fiber 2320 may have adifferent RIP than VBC delivery fiber 2340 and may be configured withdivergence altering structures as described with respect to FIGS. 20 and21 to provide additional adjustments to the divergence distribution ofbeam 2314. Thus, the beam delivered to process head 2324 will be a twiceadjusted beam 2328 having a different beam divergence profile thanadjusted beam 2314.

Process fibers 2304, 2320, and/or 2322 may comprise a RIP similar to anyof the second lengths of fiber described above, including confinementregions or a wide variety of other RIPs, and claimed subject matter isnot limited in this regard.

In yet another example, free-space optics switch 2332 may directadjusted beam 2314 to free-space optics assembly 2308 configured tochange the beam characteristics of adjusted beam 2314. Process fiber2322 may have a different RIP than VBC delivery fiber 2340 and may beconfigured to preserve (or alternatively further modify) the new furtheradjusted characteristics of beam 2314. Thus, the beam delivered toprocess head 2326 will be a twice adjusted beam 2330 having differentbeam characteristics (due to the adjusted divergence profile and/orintensity profile) than adjusted beam 2314.

In FIGS. 22A, 22B, and 23, the optics in the FFC or FFS may adjust thespatial profile and/or divergence profile by magnifying or demagnifyingthe beam 2214 before launching into the process fiber. They may alsoadjust the spatial profile and/or divergence profile via other opticaltransformations. They may also adjust the launch position into theprocess fiber. These methods may be used alone or in combination.

FIGS. 22A, 22B, and 23 merely provide examples of combinations ofadjustments to beam characteristics using free-space optics and variouscombinations of fiber RIPs to preserve or modify adjusted beams 2214 and2314. The examples provided above are not exhaustive and are meant forillustrative purposes only. Thus, claimed subject matter is not limitedin this regard.

FIG. 24 illustrates various examples of perturbation devices, assembliesor methods (for simplicity referred to collectively herein as“perturbation device 110”) for perturbing a VBC fiber 200 and/or anoptical beam propagating in VBC fiber 200 according to various examplesprovided herein. Perturbation device 110 may be any of a variety ofdevices, methods, and/or assemblies configured to enable adjustment ofbeam characteristics of a beam propagating in VBC fiber 200. In anexample, perturbation device 110 may be a mandrel 2402, a micro-bend2404 in the VBC fiber, flexible tubing 2406, an acousto-optic transducer2408, a thermal device 2410, a piezo-electric device 2412, a grating2414, a clamp 2416 (or other fastener), or the like, or any combinationthereof. These are merely examples of perturbation devices 110 and notan exhaustive listing of perturbation devices 110 and claimed subjectmatter is not limited in this regard.

Mandrel 2402 may be used to perturb VBC fiber 200 by providing a formabout which VBC fiber 200 may be bent. As discussed above, reducing thebend radius of VBC fiber 200 moves the intensity distribution of thebeam radially outward. In some examples, mandrel 2402 may be stepped orconically shaped to provide discrete bend radii levels. Alternatively,mandrel 2402 may comprise a cone shape without steps to providecontinuous bend radii for more granular control of the bend radius. Theradius of curvature of mandrel 2402 may be constant (e.g., a cylindricalform) or non-constant (e.g., an oval-shaped form). Similarly, flexibletubing 2406, clamps 2416 (or other varieties of fasteners), or rollers250 may be used to guide and control the bending of VBC fiber 200 aboutmandrel 2402. Furthermore, changing the length over which the fiber isbent at a particular bend radius also may modify the intensitydistribution of the beam. VBC fiber 200 and mandrel 2402 may beconfigured to change the intensity distribution within the first fiberpredictably (e.g., in proportion to the length over which the fiber isbent and/or the bend radius). Rollers 250 may move up and down along atrack 2442 on platform 2434 to change the bend radius of VBC fiber 200.

Clamps 2416 (or other fasteners) may be used to guide and control thebending of VBC fiber 200 with or without a mandrel 2402. Clamps 2416 maymove up and down along a track 2442 or platform 2446. Clamps 2416 mayalso swivel to change bend radius, tension, or direction of VBC fiber200. Controller 2448 may control the movement of clamps 2416.

In another example, perturbation device 110 may be flexible tubing 2406and may guide bending of VBC fiber 200 with or without a mandrel 2402.Flexible tubing 2406 may encase VBC fiber 200. Tubing 2406 may be madeof a variety of materials and may be manipulated using piezoelectrictransducers controlled by controller 2444. In another example, clamps orother fasteners may be used to move flexible tubing 2406.

Micro-bend 2404 in VBC fiber is a local perturbation caused by lateralmechanical stress on the fiber. Micro-bending can cause mode couplingand/or transitions from one confinement region to another confinementregion within a fiber, resulting in varied beam characteristics of thebeam propagating in a VBC fiber 200. Mechanical stress may be applied byan actuator 2436 that is controlled by controller 2440. However, this ismerely an example of a method for inducing mechanical stress in fiber200 and claimed subject matter is not limited in this regard.

Acousto-optic transducer (AOT) 2408 may be used to induce perturbationof a beam propagating in the VBC fiber using an acoustic wave. Theperturbation is caused by the modification of the refractive index ofthe fiber by the oscillating mechanical pressure of an acoustic wave.The period and strength of the acoustic wave are related to the acousticwave frequency and amplitude, allowing dynamic control of the acousticperturbation. Thus, a perturbation device 110 including AOT 2408 may beconfigured to vary the beam characteristics of a beam propagating in thefiber. In an example, piezo-electric transducer 2418 may create theacoustic wave and may be controlled by controller or driver 2420. Theacoustic wave induced in AOT 2408 may be modulated to change and/orcontrol the beam characteristics of the optical beam in VBC 200 inreal-time. However, this is merely an example of a method for creatingand controlling an AOT 2408 and claimed subject matter is not limited inthis regard.

Thermal device 2410 may be used to induce perturbation of a beampropagating in VBC fiber using heat. The perturbation is caused by themodification of the RIP of the fiber induced by heat. Perturbation maybe dynamically controlled by controlling an amount of heat transferredto the fiber and the length over which the heat is applied. Thus, aperturbation device 110 including thermal device 2410 may be configuredto vary a range of beam characteristics. Thermal device 2410 may becontrolled by controller 2450.

Piezo-electric transducer 2412 may be used to induce perturbation of abeam propagating in a VBC fiber using piezoelectric action. Theperturbation is caused by the modification of the RIP of the fiberinduced by a piezoelectric material attached to the fiber. Thepiezoelectric material in the form of a jacket around the bare fiber mayapply tension or compression to the fiber, modifying its refractiveindex via the resulting changes in density. Perturbation may bedynamically controlled by controlling a voltage to the piezo-electricdevice 2412. Thus, a perturbation device 110 including piezo-electrictransducer 2412 may be configured to vary the beam characteristics overa particular range.

In an example, piezo-electric transducer 2412 may be configured todisplace VBC fiber 200 in a variety of directions (e.g., axially,radially, and/or laterally) depending on a variety of factors, includinghow the piezo-electric transducer 2412 is attached to VBC fiber 200, thedirection of the polarization of the piezo-electric materials, theapplied voltage, etc. Additionally, bending of VBC fiber 200 is possibleusing the piezo-electric transducer 2412. For example, driving a lengthof piezo-electric material having multiple segments comprising opposingelectrodes can cause a piezoelectric transducer 2412 to bend in alateral direction. Voltage applied to piezoelectric transducer 2412 byelectrode 2424 may be controlled by controller 2422 to controldisplacement of VBC fiber 200. Displacement may be modulated to changeand/or control the beam characteristics of the optical beam in VBC 200in real-time. However, this is merely an example of a method ofcontrolling displacement of a VBC fiber 200 using a piezo-electrictransducer 2412 and claimed subject matter is not limited in thisregard.

Gratings 2414 may be used to induce perturbation of a beam propagatingin a VBC fiber 200. A grating 2414 can be written into a fiber byinscribing a periodic variation of the refractive index into the core.Gratings 2414 such as fiber Bragg gratings can operate as opticalfilters or as reflectors. A long-period grating can induce transitionsamong co-propagating fiber modes. The radiance, intensity profile,and/or divergence profile of a beam comprised of one or more modes canthus be adjusted using a long-period grating to couple one or more ofthe original modes to one or more different modes having differentradiance and/or divergence profiles. Adjustment is achieved by varyingthe periodicity or amplitude of the refractive index grating. Methodssuch as varying the temperature, bend radius, and/or length (e.g.,stretching) of the fiber Bragg grating can be used for such adjustment.VBC fiber 200 having gratings 2414 may be coupled to stage 2426. Stage2426 may be configured to execute any of a variety of functions and maybe controlled by controller 2428. For example, stage 2426 may be coupledto VBC fiber 200 with fasteners 2430 and may be configured to stretchand/or bend VBC fiber 200 using fasteners 2430 for leverage. Stage 2426may have an embedded thermal device and may change the temperature ofVBC fiber 200.

FIG. 25 illustrates an example process 2500 for adjusting and/ormaintaining beam characteristics within a fiber without the use offree-space optics to adjust the beam characteristics. In block 2502, afirst length of fiber and/or an optical beam are perturbed to adjust oneor more optical beam characteristics. Process 2500 moves to block 2504,where the optical beam is launched into a second length of fiber.Process 2500 moves to block 2506, where the optical beam having theadjusted beam characteristics is propagated in the second length offiber. Process 2500 moves to block 2508, where at least a portion of theone or more beam characteristics of the optical beam are maintainedwithin one or more confinement regions of the second length of fiber.The first and second lengths of fiber may be comprised of the samefiber, or they may be different fibers.

According to additional implementations described herein, there is anoptical beam system and a method for manipulating an optical beam. Forexample, FIG. 29 includes an illustration of a laser system 2900 capableof manipulating an optical beam, for example, by frequency-converting abeam and/or varying the beam characteristics of the beam. Additionally,FIGS. 30A-30B illustrate an example of a process 3000 for manipulatingan optical beam, for example, by frequency-converting a beam and/orvarying the beam characteristics of the beam.

FIGS. 29A and 29B illustrate example of laser systems having variousconfigurations of upstream and downstream components. For example, FIG.29A illustrates an example of a laser system 2900 including an opticalbeam source 2901 which can be a device that can generate a sourceoptical beam 2911; and a fiber assembly 2903, such as VBC fiber assemblyas described above, in optical communication with the optical beamsource 2901 and situated to receive and adjust one or more beamcharacteristics of the source optical beam 2911. The system can alsoinclude a nonlinear frequency-conversion stage 2902 in opticalcommunication with the fiber assembly 2903. For example, nonlinearfrequency-conversion stage 2902 can be situated to receive andfrequency-convert an optical beam, including an optical beam havingadjusted beam characteristics, from a first wavelength to one or moresecond wavelengths, to form to form an adjusted beam 2915. Accordingly,the fiber assembly 2903 in system 2900 is disposed upstream from thenonlinear frequency-conversion stage 2902.

Although system 2900 is illustrated in FIG. 29A with fiber assembly 2903disposed upstream from the frequency-conversion stage 2902, otherimplementations are not so limited. For example, FIG. 29B illustrates anexample of a laser system 2900′ including an optical beam source 2901;and nonlinear frequency-conversion stage 2902 in optical communicationwith the optical beam source and situated to receive andfrequency-convert an optical beam from a first wavelength to one or moresecond wavelengths. For example, frequency-conversion stage 2902 canchange the frequency and wavelength of the source optical beam 2911 toform a frequency-converted optical beam 2913. The system can alsoinclude a fiber assembly 2903, such as a VBC fiber assembly as describedabove. For example, fiber assembly 2903 can provide variable beamcharacteristics to frequency-converted optical beam 2913 to form anadjusted beam 2915. Accordingly, the fiber assembly 2903 in system 2900is disposed downstream from the nonlinear frequency-conversion stage2902

An optical beam source 2901 can be a diode pumped solid state laser,micro-chip laser, actively or passively q-switched laser, diode laser,mode-locked laser, gain-switched laser, fiber laser, or combination ofone or more thereof. Optical beam source 2901 can be operated with acontinuous wave output or with a pulsed or modulated output or awavelength chirped pulse output. In some examples, the light source hasa polarized output. The optical beam source 2901 can produce a sourceoptical beam 2911 having a predetermined mode profile such as a lowestorder mode profile.

The optical beam source 2901 can generate the source optical beam 2911in pulses having durations in a range of from about 1 femtosecond toabout 1000 nanoseconds. In general, a particular pulse duration may beselected based on the desired application for the output of systemsdescribed herein, or it may be selected based on cost. A pulsecompressor can be used to reduce pulse duration even further, such as toprovide pulses having durations in the picosecond and femtosecond range.

In FIG. 29A, fiber assembly 2903 can be disposed between source fiber2910 and feeding fiber 2912. Accordingly, source optical beam 2911 iscoupled into fiber assembly 2903 via source fiber 2910. In other words,source fiber 2910 can be situated to couple a source optical beam 2911,generated by the optical beam source 2901, to the fiber assembly 2903.In some implementations, the fiber assembly 2903 accepts an input beamand adjusts one or more beam characteristics of the input beam.

In FIG. 29B, nonlinear frequency-conversion stage 2902 can be disposedbetween source fiber 2910 and feeding fiber 2912. Accordingly, sourceoptical beam 2911 is coupled into nonlinear frequency-conversion stage2902 via source fiber 2910. In other words, source fiber 2910 can besituated to couple a source optical beam 2911, generated by the opticalbeam source 2901, to the nonlinear frequency-conversion stage 2902. Insome implementations, the nonlinear frequency-conversion stage 2902accepts an input beam and produces an output beam having a shorterwavelength than the input beam. In some implementations, the nonlinearfrequency-conversion stage 2902 produces an output beam having a longerwavelength than the input beam.

Nonlinear frequency-conversion stage 2902, which can be disposed withinan optical cavity, provides for the frequency conversion of an inputoptical beam. In other words, nonlinear frequency-conversion stage 2902provides for the shifting of the input optical beam's wavelength to beshifted to longer or shorter wavelengths via a frequency conversionprocess. Possible nonlinear frequency conversion processes include, butare not limited to, one or more of frequency doubling (second harmonicgeneration), frequency tripling (third harmonic generation), frequencyquadrupling (fourth harmonic generation), frequency quintupling (fifthharmonic generation), optical parametric oscillation, optical parametricamplification, or combinations thereof. In an implementation, thenonlinear frequency-conversion stage comprises a Raman shifter, whichcan comprise a crystal that provides non-linear conversion of frequencyradiation of an optical beam due, without being limited to anyparticular theory, to stimulated Raman scattering effect, and can beused for downshifting frequency of optical beams (i.e., laser radiationfrequency). In an implementation, nonlinear frequency-conversion stage2902 can comprise at least one nonlinear crystal. Exemplary nonlinearcrystals include, but are not limited to, one or more of potassiumtitanyl phosphate (KTP), monopotassium phosphate (KDP), potassiumdideuterium phosphate (KD*P), lithium triborate (LBO), cesium lithiumborate (CLBO), beta barium borate (BBO), bismuth triborate (BiBO),periodically poled lithium niobate (PPLN), lithium niobate (LiNbO₃),lithium tantalite (LiTaO₃), periodically-poled lithium tantalite (PPLT),periodically poled stoichiometric lithium tantalite (PPSLT), ZDP, bariumnitrate, cadmium sulfide (CdS), cadmium selenide (CdSe), andcombinations of such nonlinear crystals. Nonlinear frequency-conversionstage 2902 can include optics for focusing or collimating the beams,controlling beam polarization, or other components known in the art foradjusting the beams. Accordingly, a nonlinear frequency-conversion stage2902 is configured to form an output beam (e.g., frequency-convertedoptical beam 2913) having a shorter or longer wavelength than an inputbeam (e.g., source optical beam 2911).

In an implementation, one or more beam characteristics of the generated,source optical beam 2911 is/are modified and the beam is provided as anadjusted optical beam to the nonlinear frequency-conversion stage 2902.In FIG. 29A, nonlinear frequency-conversion stage 2902 is illustrated asbeing disposed between feeding fiber 2912 and delivery fiber 2914. Thus,source optical beam 2911 is coupled to fiber assembly 2903 via a sourcefiber 2910, is transmitted through fiber assembly 2903 (in which one ormore of the optical beam characteristics may be modified) and coupled tononlinear frequency-conversion stage 2902 via feeding fiber 2912.

In an implementation, the generated, source optical beam 2911 isfrequency-converted and provided as a frequency-converted optical beam2913 to the fiber assembly 2903. For example, in FIG. 29B, fiberassembly 2903 is illustrated as being disposed between feeding fiber2912 and delivery fiber 2914. Frequency-converted beam 2913 is coupledinto fiber assembly 2903 via feeding fiber 2912. In other words, feedingfiber 2912 can be situated to couple the frequency-converted opticalbeam 2913 to the fiber assembly 2903. Fiber assembly 2903 can beconfigured to vary (i.e., modify) the characteristics of an input beam(e.g., frequency-converted optical beam 2913) in accordance with thevarious examples described above

As described above, fiber assembly 2903 can include a first length offiber comprising a first refractive-index profile (RIP), a second lengthof fiber having a second RIP and being coupled to the first length offiber, and a perturbation device configured to modify one or more beamcharacteristics of an optical beam in one or more of the first length offiber, in the second length of fiber, or in the first and second lengthsof fiber. For example, Fiber assembly 2903 can comprise a first lengthof fiber 104, second length of fiber 108, and a perturbation device 110,such as that disclosed above and described in at least FIG. 1. In FIG.29A, source fiber 2910 may be separate from or comprise a portion offirst length of fiber 104 and feeding fiber 2912 may be separate from orcomprise a portion of second length of fiber 108. In FIG. 29B, feedingfiber 2912 may be separate from or comprise a portion of first length offiber 104 and delivery fiber 2914 may be separate from or comprise aportion of second length of fiber 108 or an extension of second lengthof fiber 108 that modifies, maintains, and/or confines adjusted beamcharacteristics.

As described above, beam characteristic-modified and/orfrequency-converted optical beam can be delivered to process head 2908directly via delivery fiber 2914. The process head can include guidedwave optics (such as fibers and fiber coupler), free space optics suchas lenses, mirrors, optical filters, diffraction gratings), beam scanassemblies such as galvanometer scanners, polygonal mirror scanners, orother scanning systems that are used to shape an optical beam anddeliver the optical beam to a workpiece.

FIG. 30A illustrates an example of a process 3000 for manipulating anoptical beam. Sub-processes 3003 and 3003′ represent implementations ofvarious downstream processes in which the optical beam generated atblock 3002 can be further manipulated. In block 3002, process 3000 isshown as including generating a source optical beam. In block 3004,process 3000 is shown as including frequency shifting the optical beam.In block 3006, process 3000 is shown as including modifying one or morebeam characteristics of the optical beam via a fiber assembly. Accordingto sub-process 3003, process 3000 is shown as including modifying one ormore beam characteristics of the optical beam via a fiber assembly at3006 followed by frequency-shifting the optical beam at 3004. Process3000, including sub-process 3003, can be implemented, for example, bysystem 2900 of FIG. 29A. According to sub-process 3003′, process 3000 isshown as including frequency-shifting the optical beam at 3004 followedby modifying one or more beam characteristics of the optical beam via afiber assembly at 3006. Process 3000, including sub-process 3003′ can beimplemented, for example, by system 2900′ of FIG. 29B.

The frequency-converting of the optical beam, as in block 3004,comprises shifting a wavelength of an optical beam from a firstwavelength to a second wavelength. In an implementation, the secondwavelength is longer than the first wavelength. In an implementation,the second wavelength is shorter than the first wavelength. For example,frequency-converting of the optical beam at block 3004 may comprisefrequency doubling to halve the wavelength of an input optical beam.Alternatively, frequency-converting the optical beam at block 3004 cancomprise optical parametric amplification to generate longer wavelengthsvia, for example, an optical parametric oscillator.

In an implementation, the modifying one or more beam characteristics ofthe optical beam via a fiber assembly performed at block 3006 cancomprise providing the generated beam resulting from block 3002 as asource optical beam to a fiber assembly. For example, as described aboveand illustrated in FIG. 29A, source optical beam 2911 generated byoptical beam source 2901 can be provided via source fiber 2910 to fiberassembly 2903. More specifically, the providing of the generated beam asa source optical beam to a fiber assembly can comprise coupling thegenerated optical beam to the fiber assembly via a source fiber that isdisposed between an optical beam source and the fiber assembly. Forexample, as described above and illustrated in FIG. 29A, source opticalbeam 2911 generated by optical beam source 2901 can be coupled to fiberassembly 2903 via source fiber 2910.

Returning to FIG. 30A, in an implementation of sub-process 3003, thefrequency-converting of the optical beam performed at block 3004 cancomprise providing an optical beam, such as a modified/adjusted opticalbeam resulting from block 3006, to a frequency-conversion stage. Forexample, as described above and illustrated in FIG. 29A, a beam forwhich one or more beam characteristics may have been modified by fiberassembly 2903, such as source optical beam 2911, can be provided to thenonlinear frequency-conversion stage 2902. More specifically, theproviding of the modified optical beam to the nonlinearfrequency-conversion stage can comprise coupling the modified opticalbeam from a fiber assembly comprising a first length of fiber and asecond length of fiber to a nonlinear frequency-conversion stage. Thesecond length of fiber can be coupled to the first length of fiber.Accordingly, in FIG. 29A, an optical beam having one or more beamcharacteristics modified by the fiber assembly 2903 can be coupled tononlinear frequency-conversion stage 2902, such as coupled from thesecond length of fiber to the nonlinear frequency-conversion stage 2902.

In an implementation, the frequency-converting of the optical beamperformed at block 3004 comprises providing the generated beam resultingfrom block 3002 as a source optical beam to a nonlinearfrequency-conversion stage. For example, as described above andillustrated in FIG. 29B, source optical beam 2911 generated by opticalbeam source 2901 can be provided via source fiber 2910 to nonlinearfrequency-conversion stage 2902. More specifically, the providing of thegenerated beam as a source optical beam to a nonlinearfrequency-conversion stage can comprise coupling the generated opticalbeam to the nonlinear frequency-conversion stage via a source fiber thatis disposed between an optical beam source and the nonlinearfrequency-conversion stage. For example, as described above andillustrated in FIG. 29B, source optical beam 2911 generated by opticalbeam source 2901 can be coupled to nonlinear frequency-conversion stage2902 via source fiber 2910.

Returning to FIG. 30A, in an implementation of sub-process 3003′, themodifying of the one or more beam characteristics of the optical beamperformed at block 3006 can comprise providing an optical beam, such asa frequency-converted optical beam resulting from block 3004, to a fiberassembly. For example, as described above and illustrated in FIG. 29B,the resulting frequency-converted optical beam 2913 formed at nonlinearfrequency-conversion stage 2902 by frequency converting of a generatedoptical beam, such as source optical beam 2911, can be provided to thefiber assembly 2903. More specifically, the providing of thefrequency-converted optical beam to the fiber assembly can comprisecoupling the frequency-converted optical beam to a fiber assemblycomprising a first length of fiber and a second length of fiber. Thesecond length of fiber can be coupled to the first length of fiber. Forexample, as described above and illustrated in FIG. 29B,frequency-converted optical beam 2913 formed at nonlinearfrequency-conversion stage 2902 can be coupled to fiber assembly 2903such as coupled to the first length of fiber.

As described above, in an implementation, a fiber assembly, such asfiber assembly 2903 can comprise a first length of fiber and a secondlength of fiber. As illustrated in FIG. 30B, the modifying of the one ormore beam characteristics of the optical beam, as performed at block3006, can comprise perturbing one or more of the first length of fiberand the optical beam to adjust one or more of the beam characteristicsof the optical beam at block at block 3008. The modifying of the one ormore beam characteristics can further include launching the optical beaminto the second length of fiber as in block 3010; propagating theoptical beam having the adjusted beam characteristics in the secondlength of fiber at block 3012; and maintaining at least a portion of theone or more adjusted beam characteristics of the optical beam within oneor more confinement regions of the second length of fiber at block 3014.

While various implementations are described with reference to opticalfibers, other types of optical waveguides can be used having one or moreconfinement regions having square, rectangular, polygonal, oval,elliptical or other cross-sectional shapes. Optical fibers are typicallyformed of silica (glass) that is doped (or undoped) so as to providepredetermined refractive indices or refractive index differences. Insome, examples, fibers or other waveguides are made of other materialssuch as fluorozirconates, fluoroaluminates, fluoride or phosphateglasses, chalcogenide glasses, or crystalline materials such assapphire, depending on wavelengths of interest.

Having described and illustrated the general and specific principles ofexamples of the presently disclosed technology, it should be apparentthat the examples may be modified in arrangement and detail withoutdeparting from such principles. We claim all modifications and variationcoming within the spirit and scope of the following claims.

We claim:
 1. An optical beam delivery system, comprising: an opticalbeam source; a fiber assembly situated to receive and modify one or morebeam characteristics of an optical beam, wherein the fiber assemblycomprises: a first length of fiber comprising a first RIP formed toenable modification of the one or more beam characteristics of theoptical beam by a perturbation device, and a second length of fiberhaving a second RIP coupled to the first length of fiber, the second RIPformed to confine at least a portion of modified beam characteristics ofthe optical beam within one or more confinement regions, wherein thefirst RIP and the second RIP are different; and a nonlinearfrequency-conversion stage in optical communication with the fiberassembly and situated to receive and frequency-convert an optical beamfrom a first wavelength to one or more second wavelengths.
 2. Theoptical beam delivery system of claim 1, wherein the fiber assembly isin optical communication with the optical beam source and configured tomodify one or more beam characteristics of an optical beam generated bythe optical beam source.
 3. The optical beam delivery system of claim 1,wherein the nonlinear frequency-conversion stage is further in opticalcommunication with the optical beam source and configured tofrequency-convert an optical beam generated by the optical beam source.4. The optical beam delivery system of claim 1, wherein the nonlinearfrequency-conversion stage comprises at least one nonlinear crystal. 5.The optical beam delivery system of claim 4, wherein the at least onenonlinear crystal generates a beam having second harmonic from an inputbeam.
 6. The optical beam delivery system of claim 4, wherein the atleast one nonlinear crystal comprises one or more of KTP, KDP, KD*P,LBO, CLBO, BBO, BiBO, PPLN, LiNbO₃, LiTaO₃, PPLT, PPSLT, ZDP, bariumnitrate, CdS, CdSe or combinations thereof.
 7. The optical beam deliverysystem of claim 1, wherein the nonlinear frequency-conversion stagecomprises an optical parametric oscillator.
 8. The optical beam deliverysystem of claim 1, further comprising a source fiber situated to couplea source beam, generated by the optical beam source, to the fiberassembly.
 9. The optical beam delivery system of claim 1, furthercomprising a source fiber situated to couple a source beam, generated bythe optical beam source, to the nonlinear frequency-conversion stage.10. The optical beam delivery system of claim 1, further comprising afeeding fiber disposed between the fiber assembly and the nonlinearfrequency-conversion stage.
 11. The optical beam delivery system ofclaim 1, wherein the second wavelength is longer than the firstwavelength.
 12. The optical beam delivery system of claim 1, wherein thesecond wavelength is shorter than the first wavelength.
 13. The opticalbeam delivery system of claim 1, wherein the nonlinearfrequency-conversion stage comprises a Raman shifter.
 14. The opticalbeam delivery system of claim 1, wherein the nonlinear frequencyconversion stage is contained within an optical cavity.
 15. A method formanipulating optical beams, comprising: generating an optical beam;modifying one or more beam characteristics of the optical beam via afiber assembly; and frequency-converting the optical beam, wherein fiberassembly comprises a first length of fiber and a second length of fiberand wherein the modifying of the one or more beam characteristics of theoptical beam comprises: perturbing one or more of the first length offiber and the optical beam to adjust one or more of the beamcharacteristics of the optical beam; launching the optical beam into thesecond length of fiber; propagating the optical beam having adjustedbeam characteristics in the second length of fiber; and maintaining atleast a portion of one or more adjusted beam characteristics of theoptical beam within one or more confinement regions of the second lengthof fiber.
 16. The method of claim 15, wherein frequency converting ofthe optical beam comprises shifting a wavelength of the generatedoptical beam from a first wavelength to a second wavelength.
 17. Themethod of claim 16, wherein the second wavelength is longer than thefirst wavelength.
 18. The method of claim 16, wherein the secondwavelength is shorter than the first wavelength.
 19. The method of claim15, further comprising providing the generated beam as a source opticalbeam to the fiber assembly.
 20. The method of claim 19, wherein theproviding of the generated beam comprises coupling the generated opticalbeam to the fiber assembly via a fiber disposed between an optical beamsource and the fiber assembly.
 21. The method of claim 15, wherein thefrequency converting of the optical beam comprises providing thegenerated beam as a source optical beam to a nonlinearfrequency-conversion stage.
 22. The method of claim 21, wherein theproviding of the generated beam comprises coupling the generated opticalbeam to a nonlinear frequency-conversion stage via a fiber disposedbetween an optical beam source and the nonlinear frequency-conversionstage.
 23. The method of claim 15, wherein the first length of fibercomprises a first RIP formed to enable modification of the one or morebeam characteristics of the optical beam by a perturbation device, andwherein the second length of fiber comprises a second RIP and is coupledto the first length of fiber, the second RIP formed to confine at leasta portion of the modified beam characteristics of the optical beamwithin one or more confinement regions, and wherein the first RIP andthe second RIP are different.